AD 98-11-01 R2

Discussion On October 29, 1997, the FAA issued AD 97-23-04, Amendment 39-10192 (62 FR 5993, November 6, 1997), which applies to certain Pilatus Models PC-12 and PC-12/45 airplanes. AD 97-23-04 was the result of a report from the Federal Office for Civil Aviation (FOCA), which is the airworthiness authority for Switzerland, of an instance of abnormal automatic engagement of the fuel booster pumps during normal operation of a Pilatus Model PC-12 airplane. The FOCA's investigation revealed that the fuel tank inward vent valves may fail in the closed position under certain conditions. Moisture ingestion, followed by cold soak, can lead to the fuel tank inward vent valve freezing.

AD 97-23-04 required replacing the fuel tank vent valves with modified fuel tank vent valves before the FAA superseded it with AD 98-11-01, Amendment 39-10528 (63 FR 27195, May 18, 1998). AD 98-11-01 currently requires the fuel tank vent valves replacement required by AD 97-23-04, and requires drilling a 4.8 millimeter (0.1875 inch) hole in each fuel filler cap. This AD also requires inserting the following temporary revision to the POH that specifies checking to assure that the fuel filler cap hole is clear of ice and foreign objects:

"PC-12 Pilot's Operating Handbook, Pilatus Report No. 01973-001,

Temporary Revision, Fuel Filler Cap, dated March 27, 1998." Accomplishment of the replacement is required in accordance with Pilatus Service Bulletin No. 28-003, Revision 1, dated September 30, 1997. Accomplishment of the drilling and POH insertion is required in accordance with Pilatus Service Bulletin No. 28-004, dated March 27, 1998.

AD 98-11-01 was the result of a report of an incident where the inward vent valve of the fuel tank froze closed on one of the affected airplanes that was in compliance with the fuel tank vent valves replacement requirement of AD 97-23-04. This resulted in permanent structural damage to the wing skins and ribs.

Pilatus then issued Service Bulletin No. 28-005, dated May 4, 1998, which specifies procedures for modifying the fuel tank vent valves. This modification, when incorporated, would eliminate the need for the drilling and POH requirements of AD 98-11-01.

The FAA followed by issuing AD 98-11-01 R1, Amendment 39-10608 (63 FR 34565, June 25, 1998), to incorporate Pilatus Service Bulletin No. 28-005, dated May 4, 1998, as an alternative method of compliance to AD 98-11-01 R1. Need for the Correction

The way AD 98-11-01 R1 is currently written makes it impossible for the new modified fuel vent valves to be incorporated because it does not provide the option of removing the previous replacement fuel tank vent valves as originally required by AD 97-23-04 and carried over in the current AD. In particular, paragraph (d) reads:

"(d) As an alternative method of compliance to the actions required in paragraph (b)(1) and (b)(2) of this AD, modify the fuel tank vent valve system in accordance with the Accomplishment Instructions section of Pilatus Service Bulletin No. 28-005, dated May 4, 1998." Paragraph (b)(1) requires the 4.8 millimeter hole to be drilled in each filler cap and paragraph (b)(2) requires the insertion of the temporary POH revision. Paragraph (a) requires replacement of the fuel tank vent valves.

The new modified vent valves cannot be incorporated without removing the vent valves required by paragraph (a) of the current AD. AD 98-11-01 R1 currently does not provide for this.

Consequently, the FAA sees a need to clarify AD 98-11-01 R1 to assure that the modification can be fully carried out as an alternative method of compliance for all the actions of the AD. Correction of Publication

This document clarifies the intent of the fuel tank vent valve modification specified in Pilatus Service Bulletin No. 28-005, dated May 4, 1998, as an alternative method of compliance to all of the actions of AD 98-11-01 R1. This document also adds the amendment to section 39.13 of the Federal Aviation Regulations (14 CFR 39.13).

Since this action only clarifies the intent of the fuel tank vent valve modification, it has no adverse economic impact and imposes no additional burden on any person than would have been necessary to comply with paragraph (d) of AD 98-11-01 R1. Therefore, the FAA has determined that prior notice and opportunity for public comment are unnecessary.

List of Subjects in 14 CFR Part 39 Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.

Adoption of the Amendment Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:

PART 39 - AIRWORTHINESS DIRECTIVES 1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701.

39.13 [Amended] 2. Section 39.13 isamended by removing Airworthiness Directive (AD) 98-11-01 R1, Amendment 39-10608 (63 FR 34565, June 25, 1998), and by adding a new AD to read as follows: